Method and arrangement for levelling out tension variation of an optical fibre

ABSTRACT

The invention relates to a method and arrangement for levelling out tension variation of an optical fibre when the fibre is wound on or off a reel, the basic tension of the fibre being provided by means of a dancer. To allow tension to be rapidly levelled out, the fibre is arranged to be deflected between two support and guide means by means of a transverse jet of a gaseous medium generated by a nozzle means mounted in a transverse position in relation to the direction of travel of the fibre.

BACKGROUND OF THE INVENTION

The invention relates to a method for levelling out tension variation ofan optical fibre when the fibre is wound on or off a reel, the basictension of the fibre being provided by means of a dancer. The inventionalso relates to an arrangement for levelling out tension variation of anoptical fibre when the fibre is wound on or off a reel, the basictension of the fibre being provided by means of a dancer.

In connection with treatment of optical fibres, it has been found thatwhen an optical fibre is wound on or off a reel, it is disadvantageousthat the tension of the fibre varies. Too high a tension may have adetrimental effect--either temporary or permanent--on the opticalproperties of the fibre. Too low a tension, in turn, may lead toformation of "loose loops" when the fibre is wound on a reel; such loopscause attenuation steps in the measurement results.

Tension variations are also disadvantageous in the treatment processesof the fibre. When a fibre is wound off a reel for coating, forinstance, tension variation may make the fibre vibrate, which results inunequal wall thickness of the fibre coating.

When a fibre is wound off a reel, tension variations occur, for example,because of uneven winding rate, which may result from eccentricity ofthe reel or unevenly performed winding of the fibre on the reel. Tensionvariations also occur when a fibre is wound on a reel on account of anuneven reel, eccentricity, clearings, etc. Eccentricities of guidewheels on the fibre path, clearings, friction variations of bearings,etc., also cause tension variations in the fibre. In addition, tensionvariations are caused by air flows and other ambient disturbances whichmake the fibre vibrate. Resonance frequencies must also be borne inmind. Yet another source of tension variations is forces exerted on thefibre by static electricity.

Several solutions have been provided for controlling tension variations.As a first example can be mentioned balanced lever dancers, which tendto level out tension. The disadvantage of this solution is its responsespeed, which is limited by the law a=F/m. The drawbacks of the solutionthus result from the inertial forces of mass.

A second example of known solutions is lever dancers operated by aspring, compressed air or the like. In such solutions, the proportion ofmass to force may be lower than in the previous example, wherefore a=F/mis more advantageous and the solution is faster than that of the firstexample. However, the velocity of even this known solution is not alwayssufficient for levelling out rapid tension variations.

A third example of known solutions is linear dancers. They have the samedrawbacks as the examples described above.

A fourth example is tension-controlled hauling devices, such ascapstans. These solutions have the same drawback as the examplesdescribed above, i.e. their velocity is not sufficient. In addition,such a construction is expensive--extremely expensive if the device isto be very fast.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method and anarrangement by which the drawbacks of the prior art can be obviated.This is achieved with the present invention. The method of the inventionis characterized by deflecting the fibre to compensate for tensionvariations caused by the inertia of the dancer between two support andguide means by means of a jet of a gaseous medium transverse in relationto the direction of travel of the fibre. The arrangement of theinvention is characterized in that, to compensate for tension variationscaused by the inertia of the dancer, the fibre is arranged to bedeflected between two support and guide means by means of a transversejet of a gaseous medium generated by a nozzle means mounted in atransverse position in relation to the direction of travel of the fibre.

An advantage of the invention is that it allows tension variation to belevelled out rapidly, wherefore the drawbacks caused by the tensionvariation can be eliminated efficiently. The invention thus improves theworkability of the prior art solutions: slow tension variations arecontrolled by conventional solutions, e.g. dancers, whereas rapidtension variations are controlled by the method and arrangement of theinvention. Another advantage of the invention is that it has a simpleconstruction, and thus the start-up and operating costs will be low.

In the following, the invention will be described in greater detail bymeans of preferred embodiments illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general side view of a spooler provided with an arrangementof the invention,

FIG. 2 is a general view of a first embodiment of the arrangement of theinvention,

FIG. 3 shows the embodiment of FIG. 2, viewed from the directionindicated by arrows III--III,

FIG. 4 is a general view of a second embodiment of the arrangement ofthe invention, and

FIG. 5 is a general view of a spooler provided with an arrangement ofthe invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general view of an apparatus for winding an optical fibre.The apparatus of FIG. 1 further comprises means for colouring the fibre.Apparatuses of this kind are known per se to one skilled in the art,wherefore the structure and operation of the apparatus will not bedescribed more closely herein. It will only be stated that referencenumerals 1 and 2 indicate the reels on which an optical fibre can bewound. Reference numerals 3 and 4 indicate lever dancers which provide abasic tension for the optical fibre. The lever dancers maintain anaverage tension in the fibre. Reference numeral 5 indicates thearrangement of the invention, which is shown on a larger scale in FIGS.2 and 3.

FIGS. 2 and 3 illustrate an embodiment of the arrangement of theinvention on a larger scale. The embodiment of FIGS. 2 and 3 comprisestwo wheel members 7, 8, acting as support or guide means for the fibre6, and a nozzle means 9 mounted between them. The nozzle means 9 isprovided with a fitting 10 through which a gaseous medium can besupplied to the nozzle means 9. The medium can be, for example, air. Thenozzle means 9 produces a medium jet, which is directed to the fibre togenerate a force which acts on the fibre 6 transversely in relation tothe direction of travel of the fibre, deflecting the fibre transverselyin relation to the direction of travel of the fibre. The lateraldeflection can be measured, and it can be used in the same way as adancer. The magnitude of the lateral deflection can be adjusted, forexample, by adjusting the jet. The jet may be throttled down, forinstance, so that the deflection is corrected by ocular estimate. Thenozzle means 9 can also be mounted in such a way that its distance fromthe fibre 6 can be adjusted, if necessary. The tension can naturally bemeasured, and the jet--and thereby also the tension--can be adjusted onthe basis of the measurement. The pressure of the medium may be, forexample, the normal pressure of a compressed-air system, 6 bar.

An essential feature of the invention is that it is used together withprior art dancers to eliminate their drawbacks, which are evidentparticularly in the case of rapid tension variations, as stated above.In other words, the invention is used for compensating for the tensionvariations caused by the inertia of a dancer.

The embodiment shown in FIGS. 2 and 3 can be positioned at any point ofa fibre path where it is particularly important to remove tension orvelocity variations. The invention is especially advantageous, forexample, at the point of the fibre path just before spooling, when thefibre is wound on a reel. This position is illustrated in principle inFIG. 1. Another advantageous point is immediately after the reel whenthe fibre is wound off the reel. Yet another advantageous point isbefore a coating device or a similar device.

The invention allows tension variation occurring at the lever dancerbecause of a step-like change in the speed, for instance, to beeliminated quite efficiently. Without the invention, i.e. if only alever dancer were used, the tension would fluctuate detrimentally, sincea lever dancer always has a certain structural inertia and the fibreshave a certain structural flexibility. The invention allows suchdetrimental vibration to be eliminated.

FIG. 4 shows a second embodiment of the arrangement of the invention. Inthis embodiment, the arrangement comprises only one wheel member 11acting as a support or guide means for the fibre, and a nozzle means 9adjacent to it. The idea of this embodiment is that the arrangement ismounted on a spooler in such a way that a part of the fibre path, e.g. apart of the spooler such as the dividing wheel, also serves as a supportor guide wheel for the fibre on the other side of the nozzle means 9.The embodiment of FIG. 4 operates, in principle, in the same way as theembodiment of FIGS. 2 and 3. Instead of a dividing wheel, the othersupport or guide wheel may also be the actual reel on or off which thefibre is wound.

The invention can also be applied in such a manner that the arrangementcomprises merely a nozzle means 9 which is intended to be mountedbetween two support or guide means belonging to the fibre path. In thisembodiment, the wheel members of the embodiment shown in FIG. 2 are thusreplaced, in a way, by support and guide means already existing in thefibre path, i.e. guide wheels, ceramic guide rings or similar elements.

In the examples illustrated in the figures, the fibre 6 is arranged topass between two wall portions 12, 13 at the nozzle means 9 so that thetravel of the fibre is controlled in the lateral direction. It is,however, also possible to control the travel of the fibre in the lateraldirection in some other way, for example by flow technology (e.g. airflow curtains).

FIG. 5 is a general view of a spooler provided with an arrangment of theinvention. In FIG. 5, the same reference numbers have the samesignificance as in FIGS. 1 to 4. The example shown in FIG. 5 comprises alever dancer 3 of light construction; the aim has been to make themoment of inertia of the lever dancer as low as possible. A weight wasattached to the lever dancer to generate a 30 g tension in the fibre 6,when the fibre is stationary or moves at a steady speed. An arrangement5 of the invention was mounted between the lever dancer 3 and thereel 1. In the arrangement 5, the diameters of the wheel members 7, 8were 60 mm, and the distance between their centres was 130 mm. Thepressure of the jet of compressed air from the nozzle means 9 wasadjusted to 1.8 bar; with this pressure, the fibre 6 was deflected fromits centre line by 2 to 3 mm. The deflection is shown in FIG. 5 by x. Itwas found that with a pressure of 5 bar the deflection x of the fibre 6was 7 to 8 mm. The pressure of 1.8 bar was found to be optimal forimproving the spooling result without significantly increasing thetension of the fibre.

In the testing equipment used, the typical maximum speed at which thespooling succeeded without the arrangement 5 was 600 m/min. With higherspeeds, the risk of "loose loops" on the reel became too high in view ofthe production. When the arrangement 5 was used in addition to the leverdancer, the safe maximum speed was as high as 850 m/min.

Loose loops cause attenuation steps which are easy to measure in thefibre on the reel. In normal production, such attenuation steps cannotbe allowed. In addition to the increase in step-like attenuation causedby loose loops, the quality of the spooling result can be assessed onthe basis of the magnitude the additional attenuation caused bymicrobendings of the fibre. The main principle is that the more even thequality of spooling, the fewer microbendings and the less additionalattenuation caused by them. When the arrangement 5 was used in additionto a lever dancer 3, the attenuation obtained in the tests with a singlemode fibre was 0.004 dB/km lower on the average than when only a leverdancer 3 was used. Since it can be estimated that high-quality spoolingcauses an increase of up to 0.02 dB/km in the attenuation, thearrangement 5 can be estimated to have reduced the increase inattenuation caused by spooling (microbendings) by at least 20%.

The improved spooling quality could also be observed ocularly. Theevenness of the spooling result at a speed of 850 m/min when thearrangement 5 was used was clearly better by ocular assessment than thespooling result at a speed of 600 m/min without the arrangement.

The embodiments described above are not intended to limit the inventionin any way, but the invention can be modified quite freely within thescope of the claims. Thus it will be clear that the arrangement of theinvention or its details do not necessarily have to be as shown in thefigures, but other kinds of solutions are also possible. It willtherefore be clear that the structures used for securing the arrangementcan be selected completely freely in each case. The invention is notlimited to any certain dancer type, but the invention can be used withall prior art dancers to eliminate the drawbacks of the dancer typeconcerned.

What is claimed is:
 1. In a fibre treatment process, a method forleveling out tension variation in a fibre, and wherein tension in thefibre is provided by means of a dancer; the method comprising the stepsof locating a contactless fibre deflecting device between two supportand guide means in proximity to the dancer; and deflecting the fibre bya jet of gaseous medium from said contactless fibre deflecting device,said jet directed transversely in relation to a direction of travel ofsaid fibre to thereby compensate for tension variations caused byinertia of said dancer.
 2. A method according to claim 1, includingmeasuring a magnitude of the deflection which is transverse in relationto the direction of travel of the fibre and which is caused by the jetof the gaseous medium, and using the deflection in the same way as adancer.
 3. A method according to claim 1, including measuring thedeflection of the fibre, and adjusting the jet of the gaseous mediumaccording to the measurement results.
 4. A method according to claim 1,wherein the gaseous medium is air.
 5. In a fibre treatment apparatusincluding a fibre path, a reel, and at least one dancer in said path forestablishing desired tension in the fibre, but wherein tensionvariations are caused by inertia of said at least one dancer, animprovement comprising a contactless deflecting device located betweentwo support and guide means in proximity to said at least one dancer,said contactless deflecting device comprising means for directing a jetof a gaseous medium through a nozzle toward said fibre in a directiontransverse to said fibre path such that said fibre is deflected tothereby level out the tension variations caused by said at least onedancer.
 6. An arrangement according to claim 5, wherein the support andguide means consist of two separate wheel members.
 7. An arrangementaccording to claim 5, wherein the support and guide means comprise oneseparate wheel member and a part of the fibre path which is arranged toserve as a second support and guide means.
 8. An arrangement accordingto claim 5, wherein the support and guide means comprise existingsupport and guide means of the fibre path.
 9. An arrangement accordingto claim 5, wherein the fibre is arranged to pass between two wallportions at the nozzle.
 10. An arrangement according to claim 5, whereinthe travel of the fibre at the nozzle is arranged to be controlled bymeans of flow technology.
 11. An arrangement according to claim 6,wherein the medium jet from the nozzle is an air jet.